Adhesive packaging

ABSTRACT

A method for packaging hot melt adhesive, in particular sticky hot melt adhesive or substances that are tacky at ambient temperature as a material to be packaged in a plastic film, comprising the steps:
         (a) fusing the material to be packaged;   (b) metering the fused material onto a cooling belt in portions and cooling the material to below its fusion point;   (c) removing the material portions from the cooling belt, and   (d) packaging the material portions in the plastic film,       

     the cooling belt having a textile carrier with threads which form heat conducting threads with which heat from the one flat side of the cooling belt can be transferred to the opposite side, and the carrier being embedded into a polymer matrix such that the heat conducting threads are covered as far as possible, at least on the side coming into contact with the material to be packaged.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY

This application is related to application Ser. No. 10 2010 003 896.2, filed Apr. 13, 2010 in the Federal Republic of Germany, the disclosure of which is incorporated herein by reference and to which priority is claimed.

FIELD OF THE INVENTION

The present invention relates to a method for packaging hot melt adhesive, in particular sticky hot melt adhesive or substances that are tacky at ambient temperature as a material to be packaged in a plastic film.

BACKGROUND OF THE INVENTION

Hot melt adhesives are solvent-free adhesives which for use are brought, by applying heat, into a liquid or viscous state in which they can moisten the material surfaces to be glued and to which they adhere securely after cooling and setting. Hot melt adhesives are generally made of a mixture of materials which during production are fused together and then packaged.

For use as labelling adhesives or as contact adhesion adhesives hot melt adhesives which have sticky properties at ambient temperature or below are used. These adhesives are also called PSA adhesives, and this stands for “Pressure Sensitive Adhesive”. The packaging and portioning of these sticky hot melt adhesives gives rise to problems due to the tacky surface of the adhesive portions.

Since in many cases it is desirable for the packaging of the portioned hot melt adhesive also to fuse when used in order to avoid additional working steps due to the emptying of the packaging, the film materials used must have a low fusion point and moreover must not appreciably worsen the adhesive properties of the hot melt adhesive. When using film packaging made of polymers with a low fusion point, due to the high fusion temperatures of the hot melt adhesive of for example 120 or 140° C., hot melt adhesive which is introduced directly into the film packaging while still hot separates.

In EP 0 649 718 a method is proposed according to which the hot melt adhesive is packaged and the adhesive portions thus obtained are surface-treated with an anti-adhesion substance, cooled in a cooling bath and then packaged in foil bags.

In WO 00/34129 it is proposed to cool the sticky hot melt adhesives after portioning in a water bath to such an extent that they lose their stickiness and are packaged in this state. Moreover, fatty acid derivatives are added to the water bath as an anti-adhesion agent. It is a disadvantage with this method that in this way one can only package PSA hot melt adhesives which already lose their stickiness at temperatures above the freezing point of the cooling bath, i.e. above 0° C. With both of the methods specified above the anti-adhesion agents used can, moreover, have a disadvantageous effect upon the adhesive properties of the hot melt adhesive. Finally, any water residue from the cooling path must be removed from the hot melt adhesive prior to packaging in order to rule out the presence of water when re-fusing the hot melt adhesive prior to using it.

A further method for packaging hot melt adhesive is described in DE 199 13 034, according to which the hot melt adhesive is introduced directly into a film tube which is located in a water bath during the filling process. In this way the outside of the film tube is sufficiently cooled in order to prevent immediate fusing due to the hot melt adhesive which has been poured in and is still hot. Sections of the film bag are concertinaed by means of transport rollers in order to form individual portions, and are heat-sealed at these points. It is a disadvantage with this method that the hot melt adhesive is only available in relatively large portions, and that these portions must first of all be dried after removal from the water bath. Furthermore, this method can only be implemented with packaging films which have a relatively high fusion point so that the latter do not fuse during filling despite the cooling in water.

SUMMARY OF THE INVENTION

The object forming the basis of the present invention is to provide a method by means of which the disadvantages known from the prior art can be eliminated. In particular, one should be able to dispense with the use of anti-adhesion surfaces coatings when packaging sticky hot melt adhesives. Furthermore, complex drying steps should be avoided, and it should be made possible to produce different forms of administration and portion sizes for hot melt adhesive portions.

The present object is achieved by a method of the type specified at the start, which comprises the following steps:

-   (a) fusing the material to be packaged; -   (b) metering the fused material onto a cooling belt in portions, and     cooling the material to below its fusion point so as to form     material portions; -   (c) removing the material portions from the cooling belt, and -   (d) packaging the material portions in the plastic film, the cooling     belt having a textile carrier with threads at least part of which     form heat conducting threads with which heat from the one flat side     of the cooling belt can be transferred to the opposite side, and the     carrier being embedded into a polymer matrix such that the heat     conducting threads are covered as far as possible, at least on the     side coming into contact with the material to be packaged.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

In order to fuse the hot melt adhesive the latter can be used in any form or the hot melt adhesive can be mixed from its individual components, i.e. be produced directly.

Production from the individual components can take place before or during fusion. Here the fused material is advantageously mixed by stirring, for example.

With the method according to the invention a plurality of materials can be packaged, for example resins and the like, the packaging of hot melt adhesives being a preferred application.

Within the framework of the method according to the invention the metering in portions can take place in different versions. For example, the fused material can be applied to the cooling belt in strand form, in the form of cushions, or in pastillated form. This can be implemented, for example, by means of a heated extruder, by means of one or more nozzles, such as for example in a pastillating device. Metering in portions is understood to mean both metering in defined portions, for example by weight, and metering in different portions. With portions of a consistent weight the latter can be combined to forma desired package size by counting. Portions of different weights can be combined to form desired package sizes, for example by belt weighers.

Within the framework of the present invention provision is made such that the heat conducting threads are covered as far as possible at least on the side coming into contact with the material to be packaged. This is understood as meaning that the heat conducting threads are covered practically entirely by the polymer matrix, and can only stick out of the polymer matrix at individual points, in particular the bend points e.g. with a plain weave of the textile carrier. In such a case the coverage of the heat conducting threads with the polymer matrix on the corresponding side of the cooling belt is at least 75%, in particular at least 85 to 95%, preferably 95% to total coverage. Very particularly preferably there is total coverage of the heat conducting threads with the polymer matrix on at least one side of the cooling belt.

One can also use cooling belts which have the aforementioned coverage of the heat conducting threads with the polymer matrix on both sides.

The heat conducting threads of the cooling belt enable rapid conveyance of heat to the opposite side of the cooling belt so that cooling of the material and of the hot melt adhesive by a cooling bath, such as for example a water bath, is not required. On the opposite side the heat discharged to here can be discharged for example by direct contact with a cooling medium, such as by spraying or indirectly by contact with a cooled plate or roller.

By means of the almost total coverage of the heat conducting threads with the polymer matrix of the cooling belt the heat conducting threads, which are generally at least partially formed from metal threads or carbon fibres, do not come directly into contact with the material or hot melt adhesive. This is significant in so far as, depending on the composition of the material of the cooling threads, the hot melt adhesive can have an adhesion capability of such a level that it is not possible in this case to simply remove the adhesive portions from the cooling belt.

The cooling belts that can be used according to the invention can advantageously be produced such that the textile carrier is produced first of all, for example by interweaving warp and weft threads into a plain weave. This textile carrier is then passed through a V-shaped slot in which the raw material of the polymer matrix is located which saturates the textile carrier. Solutions or dispersions of the polymers of the polymer matrix in water or organic solvents, for example, are used as a raw material for the polymer matrix.

Likewise, reactive prepolymers can be used for the production of the polymer matrix which after saturating the textile carrier abreact, thus forming the polymer matrix. In principle all reaction types, in particular radical polymerisation, polyaddition or polycondensation, can be considered for the polymerisation reaction taking place here, the latter for example with the separation of water, methanol, ethanol, acetic acid or other typical leaving groups. The substances specified above are known to the person skilled in the art from the field of adhesives and joint sealing compounds. Moreover, the polymerisation reaction can be accelerated by irradiating with UV or IR light and/or by supplying heat.

Therefore, a polymer matrix according to the invention can be produced, for example, by hardening two-component silicone at increased temperatures of approximately 200° C.

Within the framework of the method according to the invention the removal of the material portions from the cooling belt prior to packaging is achieved, for example, simply by discarding on a deflection roller. The discarding can additionally be assisted by a scraper which does not necessarily have to, but can touch the cooling belt surface. The polymer matrix of the cooling belt and the scraper should advantageously be made of a material to which the material does not or hardly adheres.

The selection of the material for the polymer matrix is ultimately dependent upon the type of material or hot melt adhesive to be packaged, and so the person skilled in the art can determine appropriate polymer matrix materials by means of simple adhesion trials. Silicone elastomers, fluoroelastomers and/or fluorosilicone elastomers are particularly preferred as material for the polymer matrix due to their anti-adhesive properties. The scraper can also be produced from these materials or also from a sheet metal which can be provided with these polymers or with a teflon layer.

Both the cooling belt and the scraper can be subjected to corona or plasma treatment in order to further reduce the adhesion of the material or the hot melt adhesive.

In an advantageous embodiment of the method according to the invention the heat conducting threads of the cooling belt are made at least partially of metals or metal alloys which are selected in particular from iron, steel, copper, aluminium, silver, brass, bronze and the like. It is also possible to use heat conducting threads made of carbon. These materials provide the cooling belt on the one hand with sufficient mechanical strength, and so dimensional stability, and on the other hand have a high heat conducting capability with which the heat of the fused material can be discharged quickly from one side of the cooling belt to the opposite side of the cooling belt.

In an advantageous embodiment of the method according to the invention the textile carrier of the cooling belt comprises a fabric in plain weave in which the heat conducting threads at least partially form warp threads. This is advantageous since with a fabric in plain weave the warp threads bend around the weft threads so that the warp threads, and so the heat conducting threads, define the upper and lower surface of the textile carrier. Despite the integration into the polymer matrix the bending points of the heat conducting threads are therefore located directly next to the surfaces of the cooling belt, by means of which good head conduction is achieved between the two flat sides of the cooling belt. Other forms of the textile carrier are also possible, such as a fabric in twill or satin weave. However, the carrier can also be made of lattice weaves or knitted fabrics.

According to a further embodiment of the method according to the invention the textile carrier has weft threads or cross threads made of a material selected from coated and/or non-coated polymer, carbon and/or metal fibres, multifilaments or monofilaments. Fibres made of nylon, aramide, Kevlar, polyesters and the like, for example, can be considered as polymer fibres. Suitable metal fibres are made, for example, of iron, steel, copper, aluminium, silver, brass, bronze or the like. Silicones, fluoro- and/or fluorosilicone elastomers, for example, can be used for the coating of the aforementioned fibres.

The warp and weft threads used within the framework of the present invention can have core threads which are wrapped at least by a wire or a polymer fibre. Alternatively, wires or polymer fibres can be stranded or braided around the core threads. The individual fibres of these threads can have a coating made of the substances specified above. It is also possible to provide warp and weft threads of the type specified above with a surface coating of the substances specified above after the wrapping, stranding or braiding.

Within the framework of the method according to the invention provision can be made such that at least sections of the cooling belt are cooled on one or both sides by means of a cooling device, preferably at least on the side which lies opposite the side coming into contact with the material or the hot melt adhesive. Cooling rolls or a cooled plate, for example, can be considered as a cooling device, over which the cooling belt is passed and which can be cooled by means of cooling agents. The opposite side can also be cooled by direct contact with a cooling medium, such as for example by spraying. For this purpose an appropriate spraying device for the cooling agent is provided. Combinations of these cooling devices are also possible.

In an advantageous embodiment of the method according to the invention the material or the hot melt adhesive is sticky at ambient temperature, in particular at 10° C. or even at 0° C., and the material and adhesive portions are preferably removed from the cooling belt in the sticky state and packaged in the plastic film. Within the framework of the method according to the invention it is therefore not necessary to cool the material or the hot melt adhesive prior to packaging to such an extent that it loses its sticky properties. For this reason, with the method according to the invention hot melt adhesives which still have sticky properties even at temperatures of below 0° C., such as for example at −5° C., can also be portioned and packaged. Here the individual adhesive portions can partially sinter together after packaging. In this way on the one hand the enlarged surface of the adhesive portions is obtained, which enables rapid fusing. On the other hand, in this way less air remains in the packaging and between the adhesive portions so that space-saving packaging is guaranteed.

In a further embodiment of the present invention the material to be packaged is a hot melt adhesive that contains a polymer component which is selected from polyolefins, in particular polyethylene, ethylene vinyl acetate copolymers, polyamides, polyesters and polyester elastomers, polyurethanes, polyacrylates and/or styrene copolymers or block copolymers or mixtures of the latter.

Furthermore, the hot melt adhesive can contain auxiliary materials selected from anti-foaming agents, wetting agents, colorants, stabilisers, softening agents, preservatives and/or resins providing stickiness, in particular colophony resins and/or derivatives of the latter.

According to a particularly preferred embodiment of the method according to the invention the plastic film is suitable for fusing synchronously with the hot melt adhesive. For this purpose the plastic film contains in particular polymers selected from polyethylene, polyvinyl acetate, polyamides, polybutadiene, polyesters, polycarbonates, atactic poly-alpha-olefins, thermoplastic polyacrylamides, polyacrylonitriles, polymethylpentenes, polyphenylene sulfides, aromatic polyurethanes, polystyrene acrylonitriles, polyethylene terephthalates and co- and terpolymers of the latter, in particular ethylene vinyl acetate.

The plastic film used within the framework of the method according to the invention preferably has a fusion temperature of 25 to 100° C., in particular 30 to 70° C., preferably 35 to 65° C. The use of these films is particularly advantageous because upon the fusion of the hot melt adhesive the latter pass quickly into the liquid form, and so release the hot melt adhesive packaged in the films for fusion. Plastic films with these low fusion points can partially not be used with the methods known thus far from the prior art because during packaging the hot melt adhesive still has such a high temperature that the film material is fused by this.

According to a preferred embodiment the plastic films used comprise at least 5% by weight ethylene vinyl acetate copolymer, for example more than 10% by weight, preferably more than 25% by weight, particularly 35% by weight or more. The respectively remaining portion is preferably formed from polyethylene. Particularly suitable are mixed films of ethylene vinyl acetate copolymer (EVA) and polyethylene (PE) with a mass ratio of ethylene vinyl acetate to polyethylene of 5:95 to 50:50, particularly of 25:75 to 40:60, preferably of 35:65.

The vinyl acetate content in the ethylene vinyl acetate copolymer used is advantageously at least 30 mole %, preferentially at least 40 mole %, preferably 30 to 70 mole %, particularly preferably from 40 to 60 mole %, very particularly preferably 50 mole %.

As well as low fusion points, these polymers and polymer mixtures of ethylene vinyl acetate and polyethylene are characterised above all by the fact that they do not generally have any negative impact upon the adhesive properties of the hot melt adhesive if the film material is fused and used together with the hot melt adhesive.

The packaging of the material and hot melt adhesive portions in the plastic film can be implemented in the simplest case by wrapping or folding in. Preferably the plastic films used within the framework of the present invention are, however, provided in the form of bags or a film tube, it being possible to produce individual bags from the latter by heat sealing and separating after packaging the hot melt adhesive.

When packaging the material portions the plastic film is generally sealed and, if so desired, the air is removed as far as possible, this being realised, for example, by sucking out the air while at the same time shaking. The closure is preferably implemented by heat sealing because no additional auxiliary materials such as clips and the like are required for this which would interfere when (re-) fusing.

The plastic films used within the framework of the present invention can in principle have any film thickness suitable for the packaging of hot melt adhesives, for example a thickness of 5 to 200 μm, in particular of 10 to 100 μm.

Advantageously neither the plastic foil nor the material portions have any surface treatment with anti-adhesive substances, such as for example silicone oils, tensides and the like. Neither is any adhesion-reducing surface treatment required, such as for example corona or plasma treatment. 

1. A method for packaging hot melt adhesive, in particular sticky hot melt adhesive or substances that are tacky at ambient temperature as a material to be packaged in a plastic film, comprising the steps: (a) fusing the material to be packaged; (b) metering the fused material onto a cooling belt in portions and cooling the material to below its fusion point so as to form material portions; (c) removing the material portions from the cooling belt, and (d) packaging the material portions in the plastic film, the cooling belt having a textile carrier with threads at least part of which form heat conducting threads with which heat from the one flat side of the cooling belt can be transferred to the opposite side, and the carrier being embedded into a polymer matrix such that the heat conducting threads are covered as far as possible, at least on the side coming into contact with the material to be packaged.
 2. The method according to claim 1, characterised in that the heat conducting threads of the cooling belt are made at least partially of metals or metal alloys which are selected in particular from carbon, iron, steel, copper, aluminium, silver, brass, bronze and the like.
 3. The method according to claim 1, characterised in that the textile carrier comprises a fabric in plain weave in which the heat conducting threads at least partially form warp threads.
 4. The method according to claim 1, characterised in that the textile carrier has weft threads or cross threads made of a material selected from coated and/or non-coated polymer, carbon and/or metal fibres, multifilaments or monofilaments.
 5. The method according to claim 1, characterised in that the polymer matrix is selected from elastic polyacrylate, silicone and fluoro- and/or fluorosilicone elastomers.
 6. The method according to claim 1, characterised in that at least sections of the cooling belt are cooled on one or both sides by means of a cooling device, preferably at least on the side which lies opposite the side coming into contact with the material to be packaged.
 7. The method according to claim 1, characterised in that the material to be packaged is sticky at ambient temperature, in particular at 10° C. or even at 0° C., and the material portions are preferably removed from the cooling belt in the sticky state and packaged in the plastic film.
 8. The method according to claim 1, characterised in that the material to be packaged is a hot melt adhesive that contains a polymer component which is selected from polyolefins, in particular polyethylene, ethylene vinyl acetate copolymers, polyamides, polyesters and polyester elastomers, polyurethanes and/or styrene copolymers or block copolymers or mixtures of the latter.
 9. The method according to claim 1, characterised in that the hot melt adhesive contains auxiliary materials selected from anti-foaming agents, wetting agents, colorants, stabilisers, softening agents, preservatives and/or resins providing stickiness, in particular colophony resins.
 10. The method according to claim 1, characterised in that the plastic film is suitable for fusing synchronously with the hot melt adhesive and/or the plastic film has a fusion temperature of 25 to 100° C., in particular 30 to 70° C., preferably 35 to 65° C.
 11. The method according to claim 1, characterised in that the plastic film contains polymers selected from polyethylene, polyvinyl acetate, polyamides, polybutadiene, polyesters, polycarbonates, atactic poly-alpha-olefins, thermoplastic polyacrylamides, polyacrylonitriles, polymethylpentenes, polyphenylene sulfides, aromatic polyurethanes, polystyrene acrylonitriles, polyethylene terephthalates and co- and terpolymers of the latter, in particular ethylene vinyl acetate.
 12. The method according to claim 1, characterised in that the plastic film comprises at least 5% by weight ethylene vinyl acetate copolymer, for example more than 10% by weight, preferably more than 25% by weight, particularly 35% by weight or more.
 13. The method according to claim 1, characterised in that the plastic film is provided as bags or a film tube and/or the plastic film has a thickness of 5 to 200 μm, in particular of 10 to 100 μm.
 14. The method according to claim 1, characterised in that the plastic film is sealed after packaging the material portions and, if so desired, the air is removed as far as possible while at the same time shaking.
 15. The method according to claim 1, characterised in that the plastic film and/or the material portions have no surface treatment with anti-adhesive substances, such as with silicone oils, tensides or the like.
 16. The method according to claim 2, characterised in that the textile carrier comprises a fabric in plain weave in which the heat conducting threads at least partially form warp threads.
 17. The method according to claim 2, characterised in that the textile carrier has weft threads or cross threads made of a material selected from coated and/or non-coated polymer, carbon and/or metal fibres, multifilaments or monofilaments.
 18. The method according to claim 3, characterised in that the textile carrier has weft threads or cross threads made of a material selected from coated and/or non-coated polymer, carbon and/or metal fibres, multifilaments or monofilaments.
 19. The method according to claim 2, characterised in that the polymer matrix is selected from elastic polyacrylate, silicone and fluoro- and/or fluorosilicone elastomers.
 20. The method according to claim 3, characterised in that the polymer matrix is selected from elastic polyacrylate, silicone and fluoro- and/or fluorosilicone elastomers. 